1. Field of the Invention
This invention relates to an air intake control system for a multi-cylinder internal combustion engine which includes intake control valves in addition to general inlet valves, the intake control valves being disposed in intake passages leading to engine cylinders respectively.
2. Description of the Prior Art
In internal combustion engines, during a start of a suction stroke, burned gases tend to flow back to intake passages from cylinders or exhaust passages due to valve overlaps. Such a back flow of burned gas lowers the charging efficiency of the engine. It is known to provide additional valves in intake passages to prevent such a back flow of burned gas.
One of prior art systems includes additional intake control valves in intake passages leading to engine cylinders respectively, and actuators for driving the additional intake control valves respectively. The additional intake control valves are controlled in response to engine operating conditions such as an engine rotational speed and an engine load. The timings of opening and closing the additional intake control valves have equal relations with the operation cycles of the engine cylinders respectively. Therefore, this prior art system can not adequately cope with a case where the engine cylinders are exposed to different air intake conditions respectively, for example, a case where the rates of air flow into the respective cylinders vary from cylinder to cylinder.
Japanese published unexamined patent application 63-65138 discloses an automotive slip control system including additional intake control valves. In the system of Japanese application 63-65138, during acceleration of an automotive vehicle, when a vehicle wheel or wheels slip, the additional intake control valves are activated to control the rates of air flow into respective engine cylinders to reduce the engine power output and thereby to suppress the slip.